Sweetening of hydrocarbons with alkali ferricyanide solutions and regeneration of the alkali solution by electrolytic oxidation



Oct. 14, 1958 R. MILLER 2,856,352

swEEIENING oF HYDROCARBONS WITH ALKALI FERRICYANIDE SOLUTIONS AND REGENERATION OF THE ALKALINE SOLUTION BY ELECTROLYTIC OXIDATION 2 Sheets/SneekI 1 Filed Jan. 27, 1955 Oct. 14, 1958 R. MILLER 2,856,352

SWEETENING OF HYDROCARBONS NITH ALKALI FERRICYANIDE SOLUTIONS AND REGENERATION OF THE ALKALINE SOLUTION BY ELECTROLYTIC OXIDATION Filed Jan. 27, 1955 2 Sheets-Sheet 2 United States Patent O SWEETENING OF HYDROCARBONS WITH ALKALI FERRICYANDE SOLUTIONS AND REGENERATION F THE ALKALI SOLU- TION BY ELECTROLYTIC OXIDATION Ralph Miller, Pleasantville, N. Y., assignor to American Development Corporation, Elizabeth, N. J., a corporation of New Jersey Application January 27, 1955, Serial No. 484,455

3 Claims. (Cl. 208-203) This invention is concerned with the treating of hydrocarbons and, more particularly, with the conversion of mercaptans to less odoriferous substances, such as disulides. Such an operation is frequently termed sweetening, and will be so designated in the description below. Petroleum products containing more than a specied concentration of mercaptan sulfur are termed sour, while those containing mercaptan sulfur concentrations below this level are termed sweet Various authorities set this concentration figure at different levels, but a generally accepted figure is 0.0005% mercaptan sulfur. The petroleum industry frequently employes relatively standard tests to determine whether or not a particular product is sweet or sour without actually determining the mercaptan sulfur concentration. The best known of these is the so called doctor test. In this test, a sodium plumbite solution of delinite composition is contacted with a sample of the product being investigated. A small quantity of flowers of sulfur is subsequently added to the mixture, and the mixture is agitated again. A change in color or the sulfur particles indicates that the sample is sour and that the test is positive. Experience has shown that this test is unnecessarily severe for certain products, and many products which were formerly processed to meet this specification are now marketed although sour by this test. In some instances, products must meet this criterion to attain customer acceptance.

A variety of sweetening processes are available. The best known are the so-called doctor process, which employs lead compounds, caustic soda, sulfur and air, and the copper chloride process. Although these processes are capable of achieving the desired results and are in widespread use, they are a perpetual source of operating difficulty. Moreover, there is as much art as science in having them operate consistently over protracted periods. In each case it has been found that the reagents eventually lose their eiectiveness to the point where they are no longer susceptible to the regeneration which is an integral part of each process. A particular disadvantage of the copper chloride process is that even trace contamination of the hydrocarbon with dissolved copper results in an iinferior product from a stability standpoint.

It is an objective of this invention to sweeten mercaptan-containing. fluids to the point that the iiuid will meet the market requirements by a process that is quickly and easily carried out, capable of being carried out at substantially ambient temperatures by a reagent exceedingly easy to regenerate and which is always in solution form.

This objective is achieved according to this invention by `contacting the mercaptan-containing fluid with an alkaline solution e. g., a sodium hydroxide or potassium hydroxide solution containing an excess amount of dissolved ferricyanide. The excess is computed on the basis of the total quantity of mercaptan to be reacted upon by the ferricyanide. It has been found that adequate contacting of the mercaptan-containing hydrocarbon with the ferricyamide-containing solution results in the disappearance of the mercaptans and the conversion of the fer- 2,856,352 Patented Oct. 14, 1958 ICC ricyanide to ferrocyanide. The ferrocyanide-containing alkaline solution is easily separated from the hydrocarbon. The separated alkaline solution containing dissolved ferrocyanide then is subjected to anodic oxidation at the anode of an electrolytic cell through which a current is being passed. At the anode, a portion of the dissolved ferrocyanide is converted to ferricyanide. The etiluent from the anode compartment of the electrolytic cell then is recycled to the contacting step with the mercaptan-containing lluid.

Extensive experimentation has shown that the simple contacting of a mercaptan-containing hydrocarbon with a substantially neutral aqueous ferricyanide solution causes but a minor disappearance of the dissolved mercaptans, and this only after an extended period of contaeting. However, when an alkaline solution of ferrocyanide is employed, the mercaptans disappear at a relatively rapid rate. It appears that the mercaptan must iirst be extracted by the aqueous solution and only after it is in the yaqueous phase is it acted upon by the ferricyanide. Because of this characteristic of the system, it is possible to contact a mercaptan-containing hydrocarbon with an alkaline solution containing dissolved ferricyanide, permit the immiscible phases to separate and, on analysis, iind that the mercaptan concentration of the hydrocarbon has markedly decreased, although mercaptans are still present, and the aqueous solution still contains some ferricyanide. If the hydrocarbon is contacted with another portion of aqueous solution similar to that used initially, the mercaptan concentration of the hydrocarbon can be diminished to a level that will meet any market requirement. Correspondingly, if the separated aqueous solution from the initial contacting is contacted with a second volume of rnercaptan-containing hydrocarbon, the aqueous solution will lose its entire ferricyanide content.

For commercial purposes, the aqueous solution may contain either sodium .or potassium hydroxide. When sodium hydroxide is employed, a concentration of about 12% NaOH is found to be eifective. Solutions both higher and lower in concentration also can be used. Solutions of higher concentration have the advantage of possessing somewhat higher conductivities and lower freezing points. On the other hand, their ability to dissolve ferrocyanide is reduced. Solutions which are lower in concentration than about 12% NaOH possess lower conductivities. Their ability to extract mercaptans does not fall olf appreciably until the NaOH concentration falls below about 8%. Such solutions can dissolve greater concentration of ferrocyanides which makes it possible to achieve greater current efficiencies in the ferricyanides conversion step. As the concentration of ferrocyanide .in the aqueous solution is increased, the ability of the solutions to dissolve mercaptans tends to decrease, thereby diminishing the rate at which the sweetening operation takes place,

` In general, solutions which are 0.1 N to 0.2 N with respect to ferrocyanide are most useful in the large majority of cases, although solutions whose composition fall outside these limits are usable.

Potassium hydroxide solutions are somewhat more useful than sodium hydroxide solutions, because KOH solutions possess greater conductivities, are better extractants for mercaptans, and are less viscous than sodium hydroxide solutions ofv equal concentrations. In addition, potassium ferrocyanide is more soluble in water than sodium ferrocyanide. The effect of common ion concentration can be eliminated by using KOH solutions in which sodium ferrocyanide is dissolved, or NaOH solutions to which potassium ferrocyanide is added.

As explained above, the regenerative part of this process consists of converting ferrocyanide to ferricyanide.` The actual' ferricyanide concentra 'on of the solutions which are employed usually is quite low. A solution which is 0.02 N in ferricyanide is amply suited to this process. Because dilute ferricyanide solution can be used, it is only necessary to convert a small fraction of the ferrocyanide in the solution toy ferricyanide in any one pass through the cell. The advantage of operating in this manner is that it permits relatively high currentv eiciencies to be secured.

There is evidence that, under some circumstances, more than one equivalent of ferricyanide disappears for each equivalent of mercaptan sulfur that disappears. However, this can be minimized by avoiding local excesses of ferricyanide in the contacting step.

The fact that more than one equivalent of ferricyanide is consumed'. foreach equivalent' of mercaptan that disappears has only one undesirable effect. lt means that more electrical energy is consumed for each mol of mercaptan acted upon than would be required if the one to one ratio is achieved. Since the total cost of the required electrical energy is small in any event, the fact that this particular item is twice or three times the possible theoretical .cost does not make any material change in the favorable overall economics of the process.

For example, 25 ml. of naphtha containing 0.015% mercaptan sulfur was treated in an active-iron-free vessel with 25 ml. of an aqueous caustic solution containing 0.1.61 milliequivalent of dissolved ferricyanide. The 25 rnl. of naphtha contained 0.080 milliequivalent of mercaptan sulfur. The two phases were permitted to separate after a short period of shaking. On analysis, it was found that the naphtha contained a total of 0.016 milliequivalent of mercaptan sulfur. That is, the mercaptan sulfur concentrationwas reduced to 0.003%. The aqueous solution contained a. total of 0.025 milliequivalent of ferricyanide. This shows that approximately 2 equivalents of ferricyanide were converted to ferrocyanide for each equivalent of mercaptan which disappeared.

These data are not' to be taken as indicating the limit of the ability of the present process to produce sweet products. For example, 25 ml. of naphtha containing 0.01% mercaptan sulfur (0.00319 N) was treated in rapid succession in an active ironfree vessel with two portions ofi aqueous solution each 25 ml. in volume. This aqueous solution was 0.00645 N with respect to ferricyanide and 3 N with respect to sodium. hydroxide. Qualitative tests showed ferricyanide present in the aqueous solution after each treatment. On analysis, the hydrocarbon contained 0.00022% mercaptan sulfur. This treated naphtha clearly is a sweet product.

The potential economy of the process can be made more readily understood by using an illustrative example. A thousand barrels. of gasoline weighs 240,000 pounds. This gasoline contains. 0.0133% of mercaptan sulfur, so that a thousand barrels of hydrocarbon contains 32 pounds of mercaptan sulfur. Ferrocyanide is converted to ferricyanide at a current eciency of 80% without difficulty. Itis assumed that two equivalents of ferricyanide are converted to ferrocyanide for each equivalent of mercaptan sulfur that disappears. (By proper contacting of aqueous solution and hydrocarbon this ratio can 'be made to approach l', but the higher gure is taken for illustrative purposes). Since 32 pounds of mercaptan sulfur are equal to a pound equivalent, then two pound equivalents of ferricyanide will be required, If these two poundy equivalents of ferricyanide are formed at a current eiiiciency of 80%, then 2.5 pound faradays of current will be needed. A poundV faraday is equal to 12,200 ampere hours. Therefore, 2.5 pound faradays are equal to 30,500 ampere hours. The alkaline solution used in this process is Sulliciently conductive so that the cell Voltage will be less than, 3 volts. The direct current requirement for converting 32 pounds of mercaptan sulfur willV approximate 91.5 kilowatt hours. At 85% efficiency for converting A. C. power toy D. C. power, the A. C. power required will approximate 110 kilowatt hours. A. C. power at a refinery will cost about'0.9 cent per kilowatt hour. Hence, the total power cost for regenerating the reagents for sweetening hydrocarbon containing as much as .013% mercaptan sulfur will be about one-tenth of a cent per barrel.

It has been stated above that by properV contacting only one equivalent of ferricyanide is consumed for each equivalent of mercaptan which disappears. That this ratio can be substantially approached is clear from thefollowingv data:

To a 12% sodiumv hydroxide aqueous solution, sufficient n-butyl mercaptan was added so that the resultant solution was 0.1075 N with respect to mercaptan sulfur. To a 12% sodium hydroxide aqueous solution, sufficient solid potassium ferricyanide was added to form a solution which was 0.1850 N with respect to ferricyanide. About 10 ml. of the mercaptan-containing solution was placed in a beaker. The ferricyanide solution was placed in a buret. The ferricyanide-containing solution then was addedl dropwise with constant stirring to the mercaptan-containing solution, until a total of 3 ml. was added. The remaining mercaptan sulfur content of the mixture was determined. It was found that the beaker contained 0.441 milliequivalent of mercaptan sulfur. Since the initial solution contained.v 1.075 milliequivalents of mercaptan sulfur, then 0.634 milliequivalent of mercaptan sulfur disappeared. A total of 0.555 milliequivalent of ferricyanide was employed to achieve this. In View of the many analyses and manipulations involved' in this experiment, this is a reasonably good check.

By employing a series of mixer-settlers or equivalentunits, it is possible to sweeten a hydrocarbon without ever having a material excess of ferricyanide present. In this way the number of equivalents of ferricyanide consumed per equivalent of mercaptan which disappears need not exceed about 1.1. For example, ml. of kerosine containing 0.013% mercaptan sulfur (the kerosine had a specific gravity of 0.781) was contacted intimately with 90 Inl. of 12% NaOH aqueous solution which also contained 35 g./l. of Na4Fe(CN)610H2O. The two solutions were separated. Based on a preliminary. experiment, 11.1 ml. of a 12% caustic solution which was 0.0195 N with respect to ferricyanide was added` to the separated caustic dropwise and with stirring. Then, 90 ml. of the resulting caustic was intimately contacted with the kerosene once more. The two phases were permitted to settle, and the caustic was withdrawn. To the separated caustic, 2.3 ml. of the 0.0195 N ferricyanide solution was added. The caustic was intimately contacted with the kerosine a fourth time andL then. the kerosene was subjected to the doctor test. The test was negative, indicating that the kerosene was sweet. The original kerosene contained 27 milliequivalents of mercaptan sulfur. A total of 27 milliequivalents of ferricyanide was consumed. This shows that by careful addition of ferricyanide to a mercaptan-containing caustic solution it is possible to quantitatively convert the mercaptans to disultides.

In carrying out the process on a commercial scale it is preferred to contact continuously theV stock to be sweetened with a solution of sodium or potassium hydroxide containing about one-tenth of a mol per liter of ferrocyanide. A similar aqueous solution which has had a part of its ferrocyanide content converted to ferricyanide is continuously injected into the system. The rate at which the ferricyanide solution is added to the system should be such that the number of equivalents of ferricyanide added to the system per unit of time shall equal the number of equivalents of mercaptan sulfur extracted from.A the stock per unit of time. By employing a suitably designed system, it is possible in this way to reduce the. mercaptan sulfur content of the stock to any desired level.

Aqueous ferrocyanide, solution, is continuously withdrawn from= the sweetening equipment at a rate equal-,t0

assasse the rate at which the ferricyanide solution is added to the contactors. The ferricyanide-containing solution is continuously passed through the anode compartment of an electrolytic cell and subjected to anodic oxidation. The anodic oxidation converts a portion, usually about of the ferrocyanide to ferricyanide. The anolyte product containing the ferricyanide then is recycled to the sweetening operation.

In the event the mercaptan sulfur content of the stock is so high as to require an undesirably large contacter for the required capacity, a series of contactors can be employed as depicted in Figure l. Since the rate at which the mercaptans are extracted by the caustic depends upon the mercaptan sulfur concentration of the stock, and since the mercaptan sulfur concentration ofthe stock diminishes as it passes through the system, decreasing volumes of the ferricyanide-containing solution are added to each contacter, thereby preventing an excessive quantity of ferricyanide from being present in any one contactor.

The ferrocyanide-ferricyande system, as explained in copending patent application Serial No. 485,200, iiled on January 3l, 1955, also is suitable for regenerating aqueous alkaline solutions employed to extract mercaptans from hydrocarbons. This operation actually reduces the sulfur concentration of the stock. Then, to meet odor requirements or other specifications, the stock may be sweetened as explained above. The sweetening process does not change the sulfur concentration of the stock. Since both processes can employ similar reagents and a common regenerative system, savings are realized with respect to capital investment, inventory, labor and the like. Unlike the two most widely employed processes, no solids in suspension need be handled. Since the regeneration process is easily controlled and regulated, there is no difficulty in maintaining the operation at the optimum point at all times.

The ferrocyanide employed herein is a water-soluble ferrocyanide which, upon anodic oxidation, is convertible to a water soluble ferricyanide. The alkali metal ferrocyanides are preferred.

Any type of cell arrangement which permits ferrocyanide in an alkaline solution to be converted to ferricyanide may be employed. One type may ybe similar in structure to the depicted in U. S. Patent 2,654,706 and may consist of a series of'electrodes made of stainless steel. Each electrode is positioned in a suitable insulated framework. A diaphragm is placed and held securely between adjoining electrodes. The diaphragm is made of inert material and so constructed that electrical ions can pass freely through it, thereby keeping the voltage drop across the diaphragm to a low value. Such a diaphragm may be made of perforated rubber, tightly woven asbestos, asbestos paper, or the like. Provision is made to permit solution to be circulated through each of the cell compartments formed between each electrode and diaphragm. The ports through which the solution leaves should be large enough to accommodate the gas formed during the electrolysis. When a current is passed through such an assembly, theelectrodes are bipolar, being anode on one side and cathode on the other. An electrolyzer of this nature can use either separate feeds for the cathode and anode compartments, or a common feed can be used. By employing one feed for the anodes and another for the cathodes it is possible to recirculate solution through the cells without subjecting any ferricyanide to cathodic reduction. It also enables the ferricyanide concentration of the anolyte to be controlled at any given value by simply adjusting the anolyte flow rate.

Another method that has been successfully employed consists of establishing two wire cloth electrodes in an insulated framework. It is convenient to position the wire cloth electrodes parallel to each other and about lAz inch apart. The plane of the cloth should be vertical. Provision is made to have the vfeed enter the space between the electrodes and flow out of the cell through the electrodes. This permits intimate contact of the solution and the electrode, insures good current efficiency, and does away with the diaphragm, thereby keeping the voltage drop to a minimum. An electrolyzer of this type possesses the disadvantage of not permitting as wide a range of ferricyanide concentration to be produced as can be made by the other type of electrolyzer, since recirculation cannot be used without subjecting some of the already-formed ferricyanide to cathodic reduction. In addition, each electrode serves either as anode or cathode, so that twice as many electrodes are required. Also, electrodes of this type are more expensive than the sheet electrodes which can be used in the other type of electrolyzer. Although this type of electrolyzer is somewhat more expensive and complicated than the other type, the higher current efficiency that can be achieved at high circulation rates makes its use attractive where power costs tend to be high. The higher current eiciencies decrease the required investment in rectifier capacity which offsets, to some degree, the higher capital cost of the wire mesh electrode type of cell compared with the sheet electrode type of cell. The cell of choice will depend upon the circumstances prevailing at any given location.

Since alkaline ferricyanide solutionsare decomposable by active iron (i. e. iron in the form of natural iron or steel, etc., but not as an inactive alloy, such as Nichrome, 18-8 stainles steel, etc.) it is desirable that contacting of such solutions be done in vessels substantially free from active iron. lt is possible however, by certain techniques, to employ iron vessels with relative impunity. For example, it is possible to feed the alkaline ferricyanide solution into the center of an iron vessel containing the mercaptan-containing solution and carry out the mixing and reaction so that the iron walls of the vessel have very little deleterious effect. However, it is preferable to handle such solutions in Vessels of inert material such as stainless steel, plastic, glass, Monel metal, rubber, concrete, or the like. The electrolyzer plates may be made of such material as vermiculite cement or perlite cement, preferably latex-impregnated to avoid solution-seepage, wherein the conductive portion of the plate may be an insert of stainless steel, or the like.

`Italso has been observed that acid oils (cresols) tend to react with alkaline ferricyanide and oils or alkaline solutions containing substantial amounts of such compounds should be avoided. Hydrogen sulfide or alkali suldes also react with alkaline ferricyanides to form free sulfur which may be deleterious in some operations wherein the free sulfur finds its way into solution in the hydrocarbon being treated. In such cases, this compound also should be avoided by a prior extraction step or similar operation.

Figure l is a diagrammatic flowsheet of the type of arrangement that is used for installations of relatively large capacity for treating stocks of relatively high mercaptan sulfur concentrations. The solid flow lines are used to indicate ferricyanide-free solutions, while the dotted lines indicate ferricyanide-containing solutions. It will be noted that the sour stock passes through line 1 to a series of mixer settlers. In each mixer 2, 3 and 4, it is contacted with a relatievly high ratio, preferably l to l, of alkaline solution containing about *0.1 mol/liter of ferrocyanide. The resulting mixture flows through lines 8, 9 and 10, respectively, into the adjoining settlers 5, 6 and 7, respectively. In the settler the stock separates from the aqueous solution and flows out of the top of the settler through lines 11 and 12, respectively,'

to the next mixer. The aqueous solution leaves the settlers 5, 6 and 7 from a bottom outlet 13, 14 and 15, respectively, for recycling to the mixer. The mercaptan sulfur concentration of the recycled caustic depends upon the mercaptan sulfur concentration of the naphtha with which it was contacted. As it ows back to the mixer, a caustic soda solution containing dissolved ferrocyanide from lino 16- and; ferricyanide; is injected into the mercap.tan-containingv caustic. The rate at which the ferricyanidercontaining solution isl pumped into the mercaptan-containing caustic is regulated; so that the number of equivalents of ferricyanide added to the caustic flowing to theV mixers is equal tothe number of equivalents ot rnercaptan` sulfur removed from the stock by the caustic. When the combined caustic solution reaches the mixer for additional mercaptan extraction, the disuldes formed by the reaction between the dissolved mercaptides and the dissolved ferricyanide pass into the hydrocarbon, Since disultdes are appreciably more soluble in hydrocarbons than in aqueous alkaline solutions.

It should be clear that the quantity of mercaptan sul fur, extracted in eachv settler will decrease as the hydrocarbony stock passes through the equipment and, for this reason, decreasing amounts of the ferricyanide-contain ing solution are pumped into the caustic being recycled.

The injection of the ferricyanide-containing caustic would continuously increase the volume of the caustic in the sweetening contactors. For this reason, caustic solution is. withdrawn from the mixer settler combinations ata rate equal` tothe rate at which the ferricyanide containing solution is introduced. The withdrawn caustic streams 1-7, 18 and 19 are combined. The combined stream then runs into storage tank 21 and is fed through line 22 to the electrolyzer 23 to reform ferricyanide which is run through line 2d into storage. Tn this manner, hydrocarbon stocks are sweetened to any desired degree and may be drawn off through line 26. Catholyte may be circulated from electrolyzer 23 through line 26 to tank 21.

When` stocks of relatively low mercaptan sulfur concentration` are to be sweetened, or when the stock to be handled is moderate in volume, a less elaborate sweetening installation suiiices. A typical small installation is shown in Figure 2. The sour stock fed through line 1 is. intimately mixed with an aqueous caustic solution in the lower portion of a tall upright vessel 2. The Lipper portion ofthe vessel is employed as a disengaging zone.

By controlling the interface level, the volume of aqueous caustic whichl leaves the vessel through line a at the top is controlled. A manifold line 4 is installed so that solutiontcan be introduced into the vessel at various locations as shown. The solution ilowing out of the top of the upright vessel flows into an inclined vessel 5', which permits the stock to be separated from the aqueous phase. The aqueous phase is withdrawn from the base of the settler through line 6 while sweetened stock is drawn oi through upper line 11. A suitable portion is led into the supply tank 8 of an electrolyzer in which ferrocyanide is convertedto ferricyanide. The ferricyanide-containing solution then is pumped through line 9 to a surge drum 2 from which point it is pumped into the lower portion of the agitator-equipped upright vessely through the manifold 4. By feeding the ferricyanide-containing solution to the. vessel. in this fashion, local excesses are minimized and substantially one equivalent of ferricyanide is converted to ferrocyanide'for each equivalent of mercaptan that disappears.. The rate at which the ferricyanide is introduced into the vessel and the rate at which the naphtha is pumped into the vessel are controlled so that the stock leaving the top of the vessel is sweet.

Any type of electrolyzer can be employed that will convert some of the ferrocyanide to ferricyanide at the rate required to convert the mercaptans to disulides. lt will be understood that pumps, valves, and other conventional equipment have been omitted in the ilowsheet and that they may be inserted wherever necessary as would he employed by those skilled in the art in carrying out the present invention.

I claim:

l. The process of sweetening a sour mercaptan-containing hydrocarbon comprising contacting in a treating Zone said hydrocarbon with an aqueous alkaline solution containing dissolved ferricyanide and ferrocyanide, maintaining a ratio of equivalents of ferricyanide to mercaptan. sulfur in saidv zone between a value of about 1.0 and 1.1, whereby mercaptans are converted to disuliides, and separating the alkaline solution from the treated hydrocarbon.

2'. The process of regenerative sweetening of a sour rnercaptan-containing hydrocarbon comprising contacting in a treating zone said hydrocarbon with an aqueous alkaline solution containing dissolved ferricyanide and ferrocyanide, maintaining a ratio of equivalents of ferricyanide to mercaptan sulfur in said Zone between a value of about 1.0 and 1.1, whereby mercaptans are converted to disullides and ferricyanide is substantially converted to ferrocyanide, separating the alkaline solution from the treated hydrocarbon, subjecting at least a portion of said solutionV to electrolytic anodic oxidationl to convert a portion of the ferrocyanide to ferricyanide, and recycling said oxidized solution to the treating zone.

3. Theprocess according to claim 1 in which the alkaline solution contains about 1:0-20 percent by weight of alkali metal hydroxide and not over about 0.2 Nl of alkali metal ferricyanide and ferrocyanide.

References Cited' in the tile of this patent UNITED STATES PATENTS 1,888,382 Heath Nov. 22, 1932 2,216,856 Short Oct. 8, 1940 2,317,600 Benedict Apr. 17, 1943 2,654,706 Gaylor Oct. 6, 1953 

2. THE PROCES OF REGENERATIVE SWEETENING OF A SOUR MERCAPTAN-CONTAINING HYDROCARBON COMPRISING CONTACTING IN A TREATING ZONE SAID HYDROCARBON WITH AN AQUEOUS ALKALINE SOLUTION CONTAINING DISSOLVED FERRICYANIDE AND FERROCYANIDE, MAINTAINING A RATIO OF EQUIVALENTS OF FERRICYANIDE TO MERCAPTAN SULFUR IN SAID ZONE BETWEEN A VALUE OF ABOUT 1.0 AND 1.1, WHEREBY MERCAPTANS ARE CONVERTED TO DISULFIDES AND FERRICYANIDE IS SUBSTANTIALLY CONVERTED TO FERROCYANIDE, SEPARATING THE ALKALINE SOLUTION FROM 